I've been searching for some time for a 3D printable chassis to fit a 2nd servo arm in my B-Robot. But the very few designs that i've been able to find do not actually have the correct dimensions so it turned out to be a waste of time and printing material. So, i decided to design my own based on the original B-Robot EVO 2 design. Personally tested! :)
You can use the same side panels from the original design, as the height of the robot stays unchanged. This modified chassis also needs the same number and type of screws and nuts, so you can re-use the other parts that you already have from the kit.
There are only 3 new parts to print for the wider chassis without requiring any other additional components: the motor plate, the electronics shelf and the top plate (optional).
UPDATE: I fixed the nut cutouts in the electronics and top plates to make them just a little bit wider so it's not too tight to put the nuts through anymore. 3D printed and tested by myself. I also attached a picture of the slightly updated electronics plate with the four nuts installed. :)
You can use a lower infill setting but i set it to a high enough value so the printed part is sturdy and doesn't flex or bend easily, especially for the motor plate.
Overview and Background
This is a tested wider version of the original chassis
The length of the electronics plate has been extended on one side of the Arduino Leonardo + Brain Shield boards (about 27 mm), so the distance between the boards and each servo is the same on both sides. This allows a second servo arm to be fitted instead of limited space for only one servo arm from the original design. There are cut-outs in some places where in the original design there were holes for screws and/or nuts but which are not needed anymore in the new design. I didn't fill the square cut-offs as it should help to save a little on printing material without comprising the rigidity of the structure.
To match the new length of the electronics plate, the motor plate and top plate have also been extended to 130 mm and 123 mm correspondingly.
Lesson Plan and Activity
Tested 3D parts
I have extended the 3D parts using TinkerCAD without losing the locations of the screws and holes as i found the software to be the easiest and most straight-forward for directly editing STL files. I have 3D printed and personally tested these new parts to verify the measurements. I mounted the electronics to check if they fit properly and also to confirm the operation of the robot. The new parts do the job - the robot balances and can be controlled without any issues. :)
For better mobility (including off-road capability) and increased accuracy in a straight line and rotating, etc, i swapped the 3D printed wheels for 5 mm hex couplings and 83 mm RC wheels.